Falconer's formula is a mathematical formula that is used in twin studies to estimate the relative contribution of genetics vs. environment to variation in a particular trait (that is, the heritability of the trait) based on the difference between twin correlations. It was first proposed by the Scottish geneticist Douglas Falconer. Falconer's formula is a mathematical formula that is used in twin studies to estimate the relative contribution of genetics vs. environment to variation in a particular trait (that is, the heritability of the trait) based on the difference between twin correlations. It was first proposed by the Scottish geneticist Douglas Falconer.